Presently, erbium-doped silicon or silicon-related materials are used for their luminescence at the wavelength of about 1.5 μm. This luminescence is due to 4I13/2-to-4I15/2intra-4-f-electron shell transition of erbium ion Er3+ that can be excited both optically and electrically.
Accordingly, erbium-doped silicon is one of the most effective materials with which silicon-based light sources may be made. Such materials may be used as films, in optic fibres or nanowires. In particular, nanowires are useful in electronic and optical devices including integrated circuit, transistors, photodetectors, biochemical sensors etc. (Generally, a nanostructure has one or two aspects of its dimensions being in the order of hundreds of nanometers. Therefore, the radius of the luminescent nano-cable, nanowire and nano-particle is typically equal to or less than 500 nms, and the thickness of nano-ribbon and layered nano-film is equal to or less than 500 nm.)
However, the efficiency of erbium-doped silicon photonics is hampered by inherent problems causing the luminescence of erbium-doped silicon to be easily quenched at between 77 K to room temperature, e.g. about 300 K. The quenching mechanisms are mainly Auger and phonon-assisted de-excitations (via Dexter mechanisms).
Auger de-excitation is the process in which one electron of the excited species gets into a higher electronic state using energy from another electron from the same species, thereby releasing the excitation energy without giving off a photon, so-called a non-radiative de-excitation. Phonon-assisted de-excitation is also a non-radiative de-excitation process, in which the energy of the excited species is released via phonons, without giving off a photon. At a concentration in excess of 1022 cm−3 in silicon or silica, erbium atoms tend to aggregate in clusters. This close proximity results in dipolar-dipolar interaction between the erbium ions, leading to a process in which an excited erbium ion de-excites non-radiatively by transferring energy to a neighboring excited erbium ion, promoting the neighboring erbium ion to an even higher excited state. This process is generally known as up-conversion, also a non-radiative de-excitation.
Quenching of erbium luminescence in erbium-doped silicon is primarily associated with energy backflow from excited erbium ions to free carriers in silicon via the three processes described above. The free carriers are, in turn, made more active by a higher temperature. As a result, erbium ion luminescence in an erbium-doped silicon is extremely weak at room temperature.
These mechanisms limit erbium excitation and are primarily responsible for thermal quenching of 1.5 μm luminescence of Er3+ ions embedded in crystalline silicon.
Furthermore, it is not easy to dope silicon or silicon-related material with erbium due to solubility limitation. This may only be achieved to an insufficiently low erbium concentration.
Therefore, it is desirable to propose a luminescent silicon structure in which these problems are reduced, eliminated or minimized.